1. Field of the Invention
The present invention in general, relates to the utilization of byproducts of incineration, i.e., dry commercial/residential sewer sludge normally disposed of in a landfill is combined with recycled high density polyethylene (HDPE) and/or polypropylene plastics (PP).
More specifically, the present invention relates to a composite formulation useful as raw material in the manufacture of composite end products, such as structural and non-structural building materials, railroad ties, shingles, decking, portable bridges, roadway paving or asphalt repair, as well as bullet proofing articles.
2. Description of the Prior Art
Concerns over dwindling landfill space have been the primary motivation in the implementation of recycling programs throughout the United States the past twenty years. Recycling efforts have been implemented to separate out reusable waste materials from waste materials that cannot be recycled often at fair expense to the municipality implementing the recycling program. The municipality promotes recycling to slow down the cost associated with the escalating of tipping fees at the landfill which have continued to escalate, principally because the volume of unrecyclable materials are continuing to escalate.
Waste not subject to recycling includes automobile tires, styrofoam, ashes, used carpet backing, mineral waste, lumber waste, a variety of cellulose fibers, and plastics. Ash has a very high disposal cost because it is typically generated from incinerators and contains heavy metals. Because of the presence of colored ink, substances such as colored paper, colored fabrics, and synthetic fabrics pose recyclability problems. Many waste forms that are not recyclable are often also not biodegradable ergo the expanding need for land fill space continues to exist in spite of the growing recycling activities throughout the country.
Because of the perceived urgency of this continuing growing problem, a plethora of applications exist in the prior art to convert some of these unrecyclable waste forms into usable products, many of which are intended to be used for building materials. Unfortunately, many of the proposed conversion processes incorporate the use of chemical compounds in processes which have limited long term stability and can be cost prohibited. For example, some of the current methods propose the use of incorporating organic compounds, such as formaldehyde, in polymeric binders. Organic binders are flammable and give off noxious fumes during settling, and have limited long term stability. Likewise, with the use of ceramic binders, which are considered cost prohibitive because these processes require high weight ratios of ceramic binder to waste form. Also, high concentrations of ceramic binder to waste form reduces flow characteristics of the slurry and leads to undesirable fast curing which is undesirable for applications in making structural components.
Products that contain significant amounts of regenerable and/or recyclable materials are taught in U.S. Pat. No. 4,947,611 to Otsuka. Otsuka discloses a wall panel containing clay in combination with straw, chaff, and palm material. The panel may optionally include hemp. Kakuk, U.S. Pat. No. 5,177,924, discloses a structural building components kit which consists of straw, chaff, and/or rice husks, using mineral additives as well as cement, lime, and/or gypsum.
Cellulose fiber has also been used as a reinforcing ingredient in thermoplastic compositions. U.S. Pat. No. 3,856,724 issued to O'Connor et al. describes a composite based on polypropylene or low density polyethylene (density 0.92) and 5% to 45%, preferably 20%, by weight of alpha-cellulose (100-mesh flock) along with some additives to make reinforced polymer composition. Arons et al., U.S. Pat. No. 3,875,088, discloses a composite material comprising 50% to 75% of a thermoplastic resin binder (ABS or rubber-modified polystyrene) and 20% to 40% of wood flour (40-mesh and 100-mesh), with the ratio of plastic to wood flour being between 1.5 and 3.0 and uses this to make pencils. U.S. Pat. No. 3,878,143 to Baumann et al., discloses a composite material comprising 63% by weight of polyvinyl chloride or polystyrene or ABS, and 30% of wood flour along with some minor additives in order to neutralize acidic gaseous matter emitted from the wood under certain temperature conditions. Hamed, in U.S. Pat. No. 3,943,079, discloses a composite material comprising thermoplastic polyvinyl chloride polymer and cellulose fiber as major components, the cellulose fibers being wood pulp or cotton linters in amounts ranging from 16% to 30% by weight of the total to incorporate discontinuous cellulose fiber into massed polymers. Armenti et al. discloses, in U.S. Pat. No. 4,165,302, filled thermoplastic resin compositions comprising low-density polyethylene, polypropylene, and other resins (in amounts ranging from 50% to 95% by weight), organic fillers (such as wood flour), and inorganic fillers (such as fly ash or calcium carbonate). The '302 patent is concerned principally with increasing the melt flow index of filled thermoplastic resin compositions rather than their mechanical properties.
It was quickly recognized that fillers, particularly cellulose fibers, do not disperse easily throughout the plastic formulations during mixing and molding. Therefore, the finished products typically do not exhibit the desirable physical characteristics ordinarily associated with fiber-reinforced plastic composites. Accordingly, this problem was dealt with in a number of patents. For example, in U.S. Pat. No. 4,250,064 to Chandler describes usage, along with low-density organic fibers (such as polyester fiber or cellulose fibers), of a combination of coarse and fine inorganic filler such as calcium carbonate (20% to 50% by weight), which makes the organic filler more easily and uniformly dispersed in a plastic matrix (preferably chlorinated polyethylene or vinyl chloride/vinyl acetate copolymer), avoiding visible clumps of fiber. Higher heat resistancy, flame retardancy, and mechanical strength were features claimed by Nakagima in U.S. Pat. No. 4,339,363. This patent disclosed that compositions of crushed wastepaper (40% to 60% by weight) and polyethylene, polypropylene, or other thermoplastic resin and their combinations, including an organic filler such as calcium carbonate, talc, barium sulfate, or the like (8% to 12%) by weight), provided the higher heat resistancy, flame retardancy, and increase mechanical strengths. Further, methods of improving dispersibility of cellulosic fibers in a thermoplastic matrix are described in U.S. Pat. No. 4,414,267 to Coran et al. as well as U.S. Pat. No. 4,559,376 to Kubat et al.
In the cellulosic-plastic composite field, increasing attention is paid to improve the physical properties, such as mechanical strength, stiffness, resistance to thermo deformation, etc. of the composite product. Motegi et al., in U.S. Pat. Nos. 4,687,793 and 4,783,493, describes elimination of moisture from cellulosic fibers (wood flour, rice hulls, wastepaper, pulp, etc.) before blending them with a thermoplastic polymer (polyethylene, polypropylene, ABS, polyvinyl, chloride, etc.) to attain greater physical properties. Also, compatibilizers markedly improve physical properties of the polymeric composite, its weatherability, and overall performance (see U.S. Pat. Nos. 4,376,144; 4,791,020; 4,820,749; and 5,008,310).
U.S. Pat. No. 5,241,795 to Giroux et al. discloses a building block product made from paper sludge, re-pulped wastepaper, or virgin paper pulp. This material is mixed with clay or portland cement, or with animal protein adhesives, or with manufactured resins or polymers.
U.S. Pat. No. 5,482,550 by Strait discloses a structural product of portland cement, recycled and ground expanded cellular polystyrene, ground cellulosic fiber, fly ash, silica fume, bentonite, water, air entrainer, paraffin wax emulsion, and rubber emulsion. This product serves as a roofing material.
Mandish and Maxwell, U.S. Pat. Nos. 5,724,783 and 5,729,936, respectively disclose wall panels made with recycled materials. Mandish's panel includes using fiberglass insulation, recycled polystyrene, rubber tires and old carpets. Maxwell discloses the use of fiber slurry composed of wastepaper, waste cardboard, straw, leaves, and grass clippings. The slurry which may contain waterproofing agents, fire retardants, anti-fungal agents, and insecticides is poured into a press form for compression.
As is clear from the preceding overview of the prior art, the use of recycled thermoplastic plastics in structural products is very limited. Items made of such plastics constitute one of the largest sources of raw material used for recycled matter. A plastic number coding is used to separate categories of recycled plastic according to their chemical composition properties and recyclability. A large number of recycled plastic items (milk and water jugs, detergent bottles, margarine tubs, bags, and yogurt containers) are composed of high and low density polyethylene classified as Codes 4 and 2. Similarly, many items (prescription bottles and plastic lids) consist of polypropylene classified as Code 5.
A need still exists in the prior art for a method to utilize or otherwise dispose of non-recyclable and non-biodegradable, benign waste without generating secondary waste streams. Although the prior art includes various thermoplastic composites based on waste materials, few of these materials are readily available on a wide spread and cost effective basis. Moreover, their proportion in the overall composite mixture tends to be somewhat low, since high proportions of non-plastic components can compromise mechanical properties. As a result, the environmental benefits offered by these compositions are limited. A need still exists for an inexpensive structural product which is partially comprised of benign waste.
Ash landfills are far more dangerous and toxic than raw trash landfills. Incinerator ash is extremely hazardous, containing dioxin and heavy metals such as lead, mercury, and cadmium. Ash landfills or monofils can never become non-toxic because most of the toxic materials in them, the heavy metals, do not bio-degrade. Accordingly, the need for a method to utilize or otherwise dispose of non-biodegradable waste such as incinerator ash without generating a secondary waste stream is paramount.